Automatic telephone-exchange system



n. DEAKIN. AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED APR... II, 1919.

UNITED STATES PA'rsNr OFFICE.

GERALD DEAXIN, OF LONDON, ENGLANDASSIGNOR TO EVESTERN 'ELECTRIC COM-PANY, INCORPORATED, OF NEW YORK, iN. Y., A CORPORATION OF NEW YORK.

AUTOMATIC TELEPHONE-EXCHANGE SYSTEM.

To all whom t may concern Be it known that I, GERALD DEAKIN, a citizenof the United States, residing at London, England, have invented certainnew and useful Improvements in Automatic Telephone-Exchange Systems, ofwhich the 4following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems and moreparticularly to improvements in full automatic and semi-automatictelephone systems.

The object orn this invention is to provide a new and improvedarrangement of private branch telephone exchanges having a pluralityottrunk lines leading from a main central office exchange7 at whichoiiice socalled iinalor connector switches are adapted to seize any oneof said trunk lines when idle. Private branch telephone exchange trunklines are usually arranged in groups on the connector' switch terminalbanks and a group of such trunks leading to a particular privatelbranchexchange is designated by a single number in the telephone directory.The connectors are adapted to be directly operated to step on to thefirst trunk terminalsin such a group and, it the associated trunk lineis busy, to automatically hunt,- due to this busy condition for theiirst idle trunk line and extend an incoming call to the operator at theprivate branch exchange.

Each of these trunk linesterminate at the .tocall the central officevand to be called by subscribers through the central ofiice. To this endsuch private branch exchange lines'are connected with lcertain trunklines 'by meansoi the usual plug and jack and by manipulating aso-called through service key, these trunlr lines and associated circuits are prepared for such through service. It is evident that undersuoli circumstances said trunk lines must be the only ones accessible.to the connector switches at the central oiiice,` that is, onlythetrunk lines connected directly to the private branch exchange linesSpecification of Letters Patent.

Application gled April 11, 1919.

Patented June 14, 1921.

serial No. 289,197.

ber of the trunk line wanted and complete the connection in the ordinarymanner.

`ln an automatic telephone exchange, where the trunk lines leading to aprivate branch exchange are only accessible by means oi automaticconnector switches, the

conditions are different and means must be provided to distinguishlbetween such trunk lines that are connected for night service and thosethat are not connected. Ordinarily, the last private branch exchangetrunk line in a group is provided with a low resistance path to batteryin shunt with the high resistance winding of the cut-off relay so thatthe hunting in the group will cease at such last trunk line. Itthistrunlr line is engaged or busy, the connector switch will send abusy signal back to the calling subscriber, but if the'last trunk isidle the connector will seize it in the usual manner and extend theconnection and ring the private branch exchange operator. The directlines are similarly equipped with a low resistance l,path to batteryand` will therefore act exactly the same Vas the last trunk line.

One feature of the present invention provides means for rendering aplurality ot private branch exchange trunk lines in a group accessibleto a directively operated connector by shunting the cut-off relays ofsuch trunks by a low resistance to battery. .Thesen trunks will therebybe available for through service in the same manner as the last trunkline in a groupand the ordinary direct lines. The numbers of the privatebranch exchange subscribers connected for .through service may be listedin the telephone directory in the same manner as ordinary subscribersexcept that they will be designated for night service only. Vfhen anyone of these numbers is called, the connector switch will be directed byselecting impulses to the number wanted in exactly the same manner aswhen a direct line is selected and the trunk line so connected will actas a direct line and the connector switch will thereby be prevented fromhunting in the group.

To accomplish this purpose, there is provided an automatic switch thatis operated lmanually by the depression of a key to cut ing a limitednumber of trunk lines, the cutting in of resistanccs may be accomplishedby means of a relay or relays in place of `the automatic switch. Theusefulness of these arrangements lies in their flexibility as the switchvmechanism or the relays .may be easily arranged to increase or decreasethe number of trunk lines controlled and any one of the trunks may beselected for this service. The fact that the control may be exercised atthe central office or at the private branch exchange is of considerableadvantage.

Another feature of this invention is the lprovision of means whereby theringing on incoming calls automatically ceases soon after a connectorswitch is set on an idle trunk line but before the private branchexchange operator answers. This is accomplished by means of relays atthe private branch exchange that operate in response to vthe ringingcurrent to connect one of the talking leads to ground for the operationof a ringing cut-olf relay at the connector switch. The trunk lines willthereby be cleared for talking when the private branch exchange operatoractuates her listening ke a Y Another feature of this invention is theprovision of means whereby, when the calling P. B. subscriber in anoutgoing call hangs up and before the P. B. X. operator removes thecorresponding plug, the trunk vlineniay be immediately seized by a con-.nector switch on an incoming call and the plug end cu-t off to preventringing current Vfrom passing through to the substation.

This is alsoV accomplished by means of the relays operating in responseto ringing current from the connector switch. The speed in which oneconnection with the private branch exchange may terminate and another beestablished is thereby considerably increased.

Another feature of this invention is the provision of means whereby thestorage battery used by lthe trunk lines and associated .circuitarrangements at the private branch exchange is charged from the centraloiiice source of direct current, whenever a trunk line is not engaged ina connection. This is accomplished by means of aV battery and anadjustable resistance connected through the line relay at the centraloffice7 and over the tip side of the line, through a contact of thesupervisory relay and a resistance'to the storage battery. The pluggingthrough of the trunk to a private branch exchange subscriber for nightservice does not interfere with the charging, but the charging circuitis cut oil' by the supervisory relay whenever the trunk line is engaged.

This and other features of the invention tending to increase theefficiency and flexibility of the private branch exchange service willbecome apparent in the following description.

In the accompanying drawing, Figure 1 represents diagrammatically anautomat-ic telephone exchange system, a private branch exchange systemand an arrangement of trunk lines as involved in this invention. Fig. 2represents a modification of the trunk line control circuit.

Tn the drawing, the parts designated B represent an automatic telephoneexchange system such as is shown and described in the U. S. patent to Frank R. McBerty, No. 1,146,583. For the filial or connector switch hasbeen substituted one having a somewhat different circuit arrangement inorder to bring out clearly its connection with this invention7 but as itdoes notas a whole form a part of this invention only such of itsfunctions as relate to the present invention, will be described; as forthe remaining functions reference may be had to the above mentionedpatent.

The part designated C represents an arrangement of various groups oftrunk line terminals and means for rendering a plurality of trunk linesaccessible to directively operated connector switches.

The parts designated D represent a private branch exchange trunk linewith suitable circuit arrangement for connecting it to a private branchexchange subscribers line indicated at E. In accordance with theabove-mentioned patent, the calling subscriber A, when desiring aconnection with a subscriber E at the privat-e branch exchangemay, bymanipulating his sending apparatus, send impulses through a line finderswitch 1() to a register control and sender equipment indicated at 11 atthe central office, which acts as a controller to govern the subsequentselecting operations necessary to extend the connection through a seriesof selector switches 12 and 13 and the final or connector switch 14 to agroupv of private branch exchange trunk lines.

lt will be assumed that an ordinary day service call is to be set up andthat all the 'selecting impulses have been sent to extend trunk line Yistov begin'. Inasmuch as the 10 tical with the corresponding operationsinoperations up to this stage are exactly identhe above-mentioned patent,it is assumed thatthev description of the operation of the connectorSwitch from this stage on and the subsequent operations necessary toextend the incoming call to a calledl subscriber at the private branchlexchange will be suiiicient to clearly Vunderstand the inventioninvolved.

The trunk-hunting operations of the connector switch begin when thesequence "switch 100 arrives in position 6, in which position the linerelay 25 is permitted to be denergized. The selector switch B has accessto direct subscribers lines, such as line 32, and also to private branchexchange trunk groups, one of which is shown consisting of the trunks33, 34 and 30. When the brushes of the selectorswitch are advanced tothe first trunk 33 of an exchange group, and such trunk is busy, thevswitch is arranged to` determine this fact` andto continue to hunt overthe succeeding trunks in search of an4 idle one. The cut-oif relays,such as relay 102, of4 all trunks preceding the last trunk 30 ofanexchange group are provided with a Ihigh resistance winding. If theiirstV trunk of the group is busy, the potential on the test terminal,applied through the high resistance winding of relay 102, is reduced tosuch an extent that the test'relay 35 cannot operate to discontinue themovement of the selector switch inthe manner `described in detailhereinafter. Consequently, the switch advancesjto the next trunk, and soon, until :an idle one is found, or until it reaches the last trunk 30in the group. The switch will stop on the terminals of this trunkregardless of the kbusy or idle condition thereof. To accom- Y plishthis feature the winding of cut-off relay 44 is shunted'by a lowresistance 43.

Due to the low resistance 43, sufficient potential existson the testterminal 45, even though the trunk is alreadyengaged to permit theenergizationof test' relay 35. Relay.35 consequently becomes operatedand terminates the hunting movement of the selector switch. The sequenceswitch 100, as hereinafter explained, advances through position.8,inwhich position a test is made to determine the busy or idle conditionof thetrunk 30. ,If the trunk is idle, full potential existson terminal45, kand the testrelay 57 is operated through its high resistancewinding to control the sequence switch 4 100 in a manner to Seize andapply ringing 'current to the tru-nk line. If, however, the

trunk -is busy, the potential on the test terminal 45 is so reduced,notwithstanding the low resistance shunt 43, that relay 57 cannotoperate and thev sequence switch 100 is controlled in a different mannerto bring about the release of the selector switch and the application ofa-busy tone back onthe calling line. Should one of the first trunks inthe group, such as trunk 33, be-idle when a test thereof is made, fullbattery potential is applied throughthe winding of cut-oi relay ,102,and the test relay 35 attracts its armatureto determine the huntingmovement of the selector switch B. A d y lConsidering the direct,subscribers line, indicatedat 32, the cut-ofi' relay 101 thereof isprovided `with a comparatively low resistanceV winding. In other words,the resistance of relay 101 corresponds to the combined resistance ofcut-oif relay 44 and resistance Y43 associated with the last trunk oaAprivate .branch exchange group. Consequently, when the brushes of theselector `switch are advanced to the terminals of a subscribers line,such as line 32, the switch does not perform a huntingV movement evenminals 30 of the last trunk line 31. As theconnector finds the trunks32, 33 and 34 busy, the private branch exchange relay 35 will not beenergized and a circuit for the power magnet 36 will be established assoon as the armature of line relay 25 reaches its back contact.V Thispower circuit extends from battery, power magnet 36, upper contact ofsequence switch contact 38, back contact and armature of relay 40, backcontact and armature of relay 25, to ground. This circuit 'keeps thepower magnet energized andthe brushes, of the switch are advanced o verthese busy trunk line terminals until they finally land on terminals30,7whena circuit is establishedl fromv battery 42, resistance 43 inparallel with battery and cut.- offrelay 44through terminal 45, brush46, private branch exchange relay 35, lower contact of sequence switchcontact 48, to ground. This energizes relay 35 and establishes a circuitfrom battery, resistance 50, armature and front contact of relay 35,test relay 40, front contact and armature of relay 52, to ground, asrelay 52 is held up as long as the connectorswitch is engaged. Testrelay 40 energizes and breaks the above-mentioned power circuit" so thatthe power magnet 36 `denergizes and stops the switch. The energizationof the test relay 40`establishes a circuit from battery, sequence switch100, upper contact `of sequence switchcontact 54,

`:front contact and ,armature of relay 40, back contact and armatureofrelay 25, to

v5'? will be energized when theV sequence switch passes through positionl8 by a circuitestablished from battery 42, resistance 43, terminal 45,brush 46, high resistance winding of relay 57, upper contact of sequenceswitch contact 48, to ground, andestablish a'locking circuit for itselfthrough its low resistance winding, front contact and armature, testrelay 40, front Contact and armature of relay 52, to ground. In thismanner relay 40 is held energized, and as the sequence switch contact 54is closed through Vposition-s 6 to 11, the sequence switch will advanceto position 12.

1n position 12 ringinglcurrent is applied from alternating-currentringing source 58, upper contact of` sequence switch contact 59, brush60, terminaly 61, contacts ofdialing key 62, retardation coil `63,condenser 64, trunk line relay 65, contacts of dialing key 62, terminal.66, brush 67, lower contact of sequence switch corntact 68, ringing-relay 69, to battery. This circuit operates trunk line relay whic'h`relay locks .up

over a circuit from battery 325, battery cut-oll`` key 95, trunk linecut off relay and holding winding of the Vrelay 65 and its front contact'and armature, to

Yground at a contact of listening key 72.

This holding circuit energizes the cut-off relay 70, which relay cutsofthe trunk leads to ylistening key 72 and extendsthe trunk leads througha condens-er 71 and relay 7 3. Relay 73 is energized over the samecircuit asrelay 65 and relayf applies at itsfront contact and armature aground to the tip side of the line. This ground completes-ajdirectcu'rrent circuit for the ringing relay 69 from battery,ringing-relayf69, lower contact of sequence switch contact 68, brush 67,terminal 66, contacts of dialing key 62, upper armature andfront Contactof cut-off relay 70, to ground at the front contact and armature ofrelay 73, to energize .ringing relay 69 .which did not respond to theabove-mentioned ringing current. The energzaton of 12 and into position15.

Position 15 is the talking position in which the ringing current is cutoil and the .talking leads are cut through as far as the trunk .linecut-off relay 70 in readiness for the operation of the listening key. Assoon as the Vringing current is cut off, the relay 73 denergizes toremove the. ground from the tip side of the line Vin order that theremay be no drain on the battery 75 after the ringing period, which ispractically instantaneous. W'hen the trunk line relay 65 was locked up,abranch circuit from battery,

relay 76, trunk line lamp 77., the front con-` tact and; armature ofrelay 65, to ground at the listeningkey 2 was completed and lamp 77lighted to indicate to the private branch exchange operator that anincoming call was present enthis trunk line.l The operator thendepresses the listening key 7 2, the immediateefiect ofwhichis'thattrunk line relay 65 'and cut-off relay 70 are released and thetalking leads extended through to the operators telephonie. The'depression oi' the listening key 72 also establishes a circuit frombattery, relay,82,itoground at the listening key 72. VThis energizesrelay 82 and a circuit is established from battery, armatureY and backcontact of supervisory relay 83, outer armature and front contact ofrelay 82, supervisory lamp 84, to ground to light this lamp -forsupervisory purposes as hereinafter described. The operation of relay 82also establishes a shunt circuitacross the i, talking leads throughretardation Vcoil 63, Vthrough-service key 85, inner armature and fron-tcontact ot relay 82'., This shunt circuit is `used for metering purposesthat forms-nofpart of this invention and need not be vfurther described.

The private branch exchange operator is operator depresses her ringingkey 86 and Vrings until the calledsubscriber answers. Then the calledsubscriber answers, a talking circuit is completed ythrough supervisoryrelay 83 and the circuit for supervisory lamp 84 is `broken therebyextinguishing the lamp.l f Y At the'end of the conversation and when theCalled. Subscriber hangs up his receiver,

switch to be released when the the calling subscriber hangs up, whichact results in the denergizaton of relay 52, as is fully described intheA beforementioned patent.

The denergization of relay 52 establishes a circuit from battery,sequence switch 100, upper contact of sequence switch contact 56, backYcontact and armature of relay 52, to ground, to move sequenceswitch-100 out of position 15 into position 17. In position 17, acircuit l, is established from battery sequence switch 100, lowercontact of sequence switch contact 54, back contact and amature of relay25, to, ground, to move sequenceV switch 100 into position 18. In

Vposltion 18 ,a circuit is established from battery, power magnet 36,upper contact of` sequence switch contact 38, back contact and armatureof relay 40, back contact and' armature of relay to ground, to operate4power `magnet 36 and drive the connector switch back to normalposition. On reaching normaln position, a circuit is established frombattery, relay 25, upper contact oi sequence switch contact 89, normalcontact 90, to ground. Relay 25 energizes and establishes acircuit frombattery, sequence switch 100, upper contact of sequence switch contact74, and front contact and armature of relay 25, to ground, to drivesequence switch 100 back to position one.

In preparing the private branch exchange trunk lines for night service,that is, making a number .of trunks accessible for incoming calls, it isonly necessary to convert them to direct lines by. inserting a lowresistance shunt path to battery in parallel with the high resistancecut-off relay winding to battery. Thel trunks that are to be used fornight service are then connected with the private branch exchangesubscribers who are to receive or send calls directly during the absenceof the private branch exchange operator. In order to prevent the trunklines from being cut off from the connected private branch exchangesubscribers by relay in the manner heretofore described when seized bythe connector switch, the throughservice key and battery cutoff key areoperated.

A trunk line 32 in the group of trunks at 20 is typical of the ordinarytrunk line and trunks 33 and 34 are ytypical of the trunk lines to whicha resistance shunt may be added., By switching inA these resistances ontrunks 33 and 34, or any other trunk in the group, such trunks will bemade available for through service. A sequence switch 200 is used forthis purpose having sequence switch contacts, such as 201 and 202,closed in positions 2 to 18,4 to 18, etc., a normal contact 203 closedjust after position 1 to just before position 18, and a contact 204closed in position 1 and position 18. To control the sequence switch200, key 206 at the private branch exchange and thelrelay 208 at thecentral ofiice, are provided. To

out in resistances, the private branch ex? change operator depresses key206 and a circuit is establishedl from battery, relay 208, key 206, toground. This energizes relay 208 and a circuit is established fromvbattery, sequence switch 200, upper ContactA of sequence switch Contact204, front contact and armature of relay 208, to ground.

This starts the sequence switch 200 whichA completes a circuit foritself through its normal contact 203, to ground, and continues to moveor rotate until it reaches the eighteenth position when the circuit isbroken and the sequence switch stops. The rotation of sequence switch200 from position 1 to 18 cuts in the resistance 210 in position 2,resistance 211 in position 4, etc. The resistances 210 and 211 are equalin value to that of resistance 43. Hence, for example, when resistance210 is placed in shunt around the winding of relay 102 the electricalcondition on the test terminal of trunk 33 is changed to conform exactlywith that on the last trunk 30 of the group. Conseiop quently, -whenVthe brushes of the selector switch B are'advanced to terminals of trunkthe same purpose with respect to the nextA trunk 34. It is evident thatall the resistances could be inserted at once but it is often preferableto switch them in succession. Selection of trunks for night service neednot be confined to the trunks 33 and f 34 and need not be made in anyparticular order as Vthe trunks selected may be scattered over the groupby removing sequence switch contact, such as 201 or 202, or by f theaddition of others.

In Fig. 2 is shown a key 215 that may be substituted for key 206 andrelay 208 and` the leads 216 and 217 may be connected at 218 and 219,respectively, to the sequence switch contact 204, in case the controlover the night service is to be exercised by an attendant, such aswire-chief at the central a limited number of trunk lines and inV which.night service is confined to two or three trunks.

It is seen by this arrangement of the night and through service that nohunting will take place at the connector switch but that the connectorswill be directed toa particular private branch exchange trunk by means.of'selective impulses in the same manner as Vto a direct'line and thatthere will be no distinction between aprivate branch exchange trunk lineconnected to a private branch exchange subscriber andthe line leadingdirectly to a regular subscriber. VThe relay 'will immediately beenergized when the brushes of the connector are set on a selectedprivate branch exchange trunk, and as here inbetore described, thesequence switch will be driven toward the twelfth position. In case theline is idle, the call will proceed, as already described, but in casethe wanted subscriber-is busy, the sequence switch 100 will st op inpositie-n 10, for it will be remembered that it depends on theenergizationV of relay 57 for maintaining'the relay 40 operated afterthe sequence switch passes the eighth position. Therefore, incase theline is busy, the rela-y 57 will not be energized` as there will be alow resistance pathV to ground through the test relay 57 of theconnectoralready connectedto a multiple of the test` terminals of thistrunk. This path to ground is of low enough resistance to prevent asuiiicient current from flowing through the highresistance winding ofrelay 57 of this connector. Consequently, the sequence switch will stopwhen it Varrives in position lO as the relay 40 that was denergizedalready in the eighth position, has broken the energizing circuit forthe sequencefswitch 100 at its front contact and armature. In position10, a busy tone is sent back to the calling subscriber through inductioncoil 250, the primary circuit being established from busy tonealternating current source 251, upper contact of sequence switch contact252, primary circuit of induction coil 250, to ground. When the callingsubscriber hangs up, due to this busy tone, relay 52 de'e'nergizesV and-a circuit is established from battery, sequence switch 100, upperContact of sequence switch contact 56,

back contact and armature of relay 52, to

ground, Vto' move sequence switch 100 into .position 11.V InV position11, a circuit is established from battery, power magnet,

upper contact of sequence switch contact 38, back contact and armatureof relay 40, back contact and armature of relay 25, to ground,

to drive the connector switch back to nor-V relay 52, to ground, todrive sequence switch 100 into'position 17. In position 17, a cirf cuitis Yestablished from.Y battery, sequence switch 100, lower contact ofsequence switch Contact 5a, back contact and armature of relay 25, toground, to drive sequence switch 100 into position 18. In position 18, acircuit is established from-battery, relay 25,

upper contact ci' sequence switch contact 89,

normal cont-act 90, to ground, to again energize relay 25 and establisha circuit from battery, sequence switch 100, upper contact of sequenceswitch contact 74, front contact and armature of relay 25, to ground, todrive sequence switch 100 out of position 18 into normal position. Y

In a call outgoing from a private branch exchange, the private branchexchange subn scriber, by removing his receiver from the hook, lightsthe lamp 301 and the operator answers by inserting plug 78 in jack 79which extinguishes the lamp 301. The operator then operates listeningkey 72 and ascertainsr the number ot the subscriber wanted. rIhe dialingof a number may be done by the private branch exchange operator byoperating dialing key 62 which connects the operators sender 305 tothetrunk line and the retardation coil 306 to the plug en d of the trunkline. Vi7hen the operator has finished dialing the number, the dialingkey returns to normal andthe connection which has proceededautomatically througha line finder indicated at 310 at the centraloflice is extended to the wanted subscriber in the usual manner.

When the trunk ,lines are prepared for through or night service that areconnected i io to certain private branch exehangesubscribcrs and thethrough service key 85 is operat- 1: private branch scribed, thereleaseof the connector is controlled by the hanging up of the calling sexchange subscribers receiver. A The circuit for charging of the storagebattery at 325 extends from battery 7 5, adjustable resistance 326, linerelay 327, tip

yside of trunk line 31, contact of dialing key 62, upper armature andback contact of cutoffrelay 70, outer back contact and armature of relay82, armature and back contact of relay 83 resistance 329, key 330,battery v325 to ground. The charging of the battery is not interferedwith at any time, except when the truck circuit is engaged, when thesupervisory relay 83 is energized and breaks the battery circuit at itsarmature and back contact. The plugging up of the trunk line for nightservice has no effect on the battery charging circuit, as only thebattery cut-oli key 95 is operated to cut oi the battery from relays 70and 82, trunk lamp 77 and alarm relay 7 6.

What I claim is:

1. In a telephone exchange system, subscribers lines, trunk lines, anautomatic switch Jfor selecting any of said lines, means for placing agiven electrical condition on said subscribers lines, means for placinga different electrical condition on the trunk lines, means responsive tosaid electrical conditions for controlling the operation of saidautomatic'switch, and means for automatically changing the condition onsaid trunks to correspond to the electrical condition on saidsubscribers lines to render said trunks of the same identity as thesubscribers lines.

2. In a telephone exchange system, subscribers lines, trunk lines, anautomatic switch for selecting any of said lines, means for placing agiven electrical condition on said subscribers lines, means for placinga diHerent condition on the trunk lines,means responsive to saidelectrical conditions for controlling the operation of said switch, andan auxiliary switch for changing the condition on said trunks tocorrespond to the condition on the subscribers lines to render saidtrunks of the same identity as the subscribers lines.

3. Ina telephone exchange system, subscribers lines, an operatorsposition, trunk leading to said position, an automatic switch forselecting said lines and trunks, means `for placing a given electricalcondition on said lines, means forplacing a different condition on saidtrunks, means responsive to said electrical conditions for controllingsaid switch, and means controlled manually by the operator for changingthe condition on said trunks to correspond to the condition on saidlines to render said trunk and lines of the same identity.

4. In a telephone exchange system, subscribers lines, trunk linesnormally distinguished from the subscribers lines, a switching deviceoperable to engage any one of said lines, automatic means at one end ofthe trunk for eliminating the normal distinction between a trunk and asubscribers line whereby said trunk may be engaged as a subscribersline, and means at the other end of said trunk for controlling saidautomatic means.

5. In a telephone exchange system, subscribers lines, trunk linesnormally distinguished from the subscribers lines, a switching deviceoperable to engage any one of said lines, automatic means foreliminating in succession Athe normal distinction between said trunksand subscribers lines whereby said trunks may be engaged as subscriberslines, and manual means for controlling said automatic means.

6. In a telephone exchange system, a plurality of trunk linesinterconnecting two telephone exchanges, a switching device operable toengage any one of said trunks, means at said switching device forapplying ringing current to a trunk, and means at the distant end of atrunk for completing a circuit including only one of the talking leadsof said trunk to disconnect the ringing current.

7. In a telephone exchange system, a plurality of trunk linesinterconnecting two telephone exchanges, a switching device operable toengage any one of said trunks, means for applying ringing current to atrunk, means at the distant end of a trunk responsive to said ringingcurrent, and means controlled from said responsive means over one sideof the talking leads of the trunk to disconnect said ringing current.

8. In a telephone exchange system, a plurality of trunk linesinterconnecting two telephone exchanges, a switching device operable toengage any one of said trunks, means for applying ringing current to atrunk, means at one exchange for disconnecting the ringing means, meansat the other exchange responsive to said ringing current, and means atsaid second exchange controlled by said ringing responsive means tooperate said ringing disconnecting means over one side of the talln'ngleads of the trunk.

9. In a telephone exchange system, a plurality of trunk linesinterconnecting two telephone exchanges, a switching device op-v erableto engage any one of said trunks, means for applying ringing current toa trunk, a relay at one exchange for disconnecting the ringing means, arelay mechanism at the other exchange responsive to said ringingcurrent, and means operated by said relay mechanism for connecting aground over one side of talking leads to control the ringing relay.

10. In atelephone exchange system, a plurality of trunk linesinterconnecting twov telephone exchanges, a switching device operable toengage any one of said trunks, means for applying ringing current to atrunk, means for connecting a subscriber at the distant end of a trunk,and automatic means responsive to the ringing current for cutting offthe subscriber from the trunk during the ringing perid.

11. In a telephone exchange system, a plurality of trunk linesinterconnectingtwo v telephone exchanges, a switching device operable toengage any one of Vsaid trunks, means for applying'ringing current to atrunk, an operatorspositon at the distant end of a trunk, automaticmeans responsive to the ringing current for cutting 0E the 0peratorsposition from the trunk, and a mauual means for restoring the connectionto the operators position.

l2. In a telephone exchange system, a plurality of trunksinterconnecting two exchanges, a switching device operable to engage anyone of said trunks, a charging means including an adjustable resistanceand a source of direct current at one exchange, an adjustable resistanceand storage battery atl the other exchange, and a circuit in-vterconnecting said batteries over one talking lead of a trunk.

In Witnessy whereof, I hereunto subscribe my name this 12th day ofFebruary, A. D.,

- GERALD DEAKIN.

